1. Field of the Invention
The present invention relates to a sealing structure of a plasma processing apparatus, a sealing method, and a plasma processing apparatus including the sealing structure.
2. Description of the Related Art
Plasma technology is being widely used for manufacturing variety of semiconductor devices, such as integrated circuits, liquid crystal displays, solar batteries, etc. Plasma technology is used in thin film formation, thin film etching, or other operations included in a semiconductor manufacturing process. However, a highly accurate plasma process, for example, a super-fine processing technique, is required to achieve high-performance, high-functional products. In particular, microwave plasma processing apparatuses using microwave plasma have attracted much attention.
In a plasma process, stable plasma generation is essential, and vacuum maintenance is important to achieve stable plasma generation. When a plasma process is performed, sealing prevents leakage of air or gas from a plasma generation chamber and entry of external air into the plasma generation chamber, thereby maintaining the plasma generation chamber in an airtight or vacuum state. An O-ring generally used in such sealing is prone to deterioration when the O-ring is exposed to plasma atmosphere, leading to generation of particles or degradation of sealing.
Japanese Laid-Open Patent Publication No. hei 6-112168 (hereinafter, referred to as reference 1) discloses a plasma processing apparatus which performs a uniform plasma process. A reaction vessel is made airtight through a conductive O-ring, by an upper electrode that forms a cover of the grounded reaction vessel. Even when the upper electrode is bent, the upper electrode is electrically connected to the reaction vessel, and thus the reaction vessel is grounded. Thus, no electrical disturbance occurs as high frequency, and no noise is generated. Consequently, a reaction gas is homogenously converted into plasma and thus a uniform plasma stream is generated. Accordingly, a semiconductor wafer is uniformly plasma-processed.
Japanese Laid-Open Patent Publication No. 2000-182958 (hereinafter, referred to as reference 2) discloses a vacuum device which detects external leakage in an early stage in order to minimize damage. The vacuum device includes a vacuum chamber, a vacuum chamber sealing member, and an inert gas seal-in member between the vacuum chamber sealing member and external air. The inert gas seal-in member prevents external air from entering the vacuum chamber when leakage occurs in the vacuum chamber. The inert gas seal-in member includes a first pressure monitoring mechanism which monitors the pressure of the inert gas seal-in member, and a second pressure monitoring mechanism which monitors the pressure of the vacuum chamber. Therefore, the vacuum device is able to detect leakage in an early stage.
Japanese Laid-Open Patent Publication No. 2004-99924 (hereinafter, referred to as reference 3) discloses a vacuum treatment system capable of improving corrosion resistance and completely preventing intrusion of air into a chamber. An outer sealing member and an inner sealing member are fitted into an outer groove and an inner groove, respectively, which are formed concentrically in contact parts where a wall and a ceiling plate that constitute the chamber abut on each other. A passage through which the outer sealing member and the inner sealing member communicate with each other is formed, and a helium gas, which supplies a pressure exceeding an atmospheric pressure, is filled into the passage. Therefore, the vacuum treatment system can improve corrosion resistance and completely prevent intrusion of air into the chamber.
Japanese Laid-Open Patent Publication No. 2004-141803 (hereinafter, referred to as reference 4) discloses a plasma processing apparatus which prevents particle generation caused by deterioration of an O-ring and also prevents deterioration of a sealing property. A gate valve is formed between a reaction chamber and a transfer chamber, and thus a metal mesh-shaped O-ring and a fluororesin-based O-ring are formed on the side of the reaction chamber and on the side of the transfer chamber, respectively. Therefore, plasma atmosphere is kept in the reaction chamber of the plasma processing apparatus.
A method of using two O-rings with two different functions is well known as a method of preventing reduction of the sealing property by suppressing deterioration of an O-ring as much as possible. However, this well-known method does not consider blockage of microwaves. In addition, an abnormal electric discharge occurs between the two O-rings, and thus plasma may be unstable.
The reference 2 focuses on detecting degradation of an O-ring and preventing leakage from occurring in a vacuum chamber, but provides no particular measures to prevent deterioration of the O-ring. The reference 3 protects an O-ring from being exposed to plasma atmosphere by using an inert gas, but a relatively expensive helium gas should be used as the inert gas so that the inert gas can penetrate through the O-ring.